1. Field of the Invention
This invention relates to a centrifugal artificial heart pump for surgical implantation in a human patient, more specifically to a centrifugal artificial heart pump whose rotor is suspended in a noncontacting state by magnetic force.
2. Description of the Prior Art
Artificial heart pumps can be classified into the reciprocating type, the rotary displacement type, and the turbo type that operates by rotational flow. Typical of the turbo type that operates by rotational flow is the centrifugal type.
Artificial heart pumps of the centrifugal type are generally equipped with a casing, a rotor disposed inside the casing, a motor for rotating the rotor, a blood flow channel for introducing and guiding the flow of blood, and an impeller that rotates integrally with the rotor for imparting centrifugal force to the blood flowing in through the blood flow channel formed in the casing.
The prior art centrifugal type artificial heart uses ball bearings for rotatably supporting the rotor provided with the impeller. With this system, however, blood flow is liable to stagnate in the vicinity of the ball bearing. Since the formation of stagnant blood is known to be a primary cause of blood coagulation (thrombogenesis), an artificial heart pump that is susceptible to such stagnation has a major defect.
For eliminating this drawback, there have been proposed pumps whose rotors are suspended in a noncontacting state by magnetic force.
U.S. Pat. No. 4,688,998, for example, teaches a pump whose rotor is suspended by electromagnets. The pump's magnetic suspension system constantly maintains the rotor in the proper attitude by regulating the current supplied to the electromagnets so as to control their magnetic force. With this system for supporting the rotor by the force of electromagnets, however, there is a danger that anomalies arising in the control system during pump operation may disturb the attitude of the rotor and, as a result, disrupt the normal flow of blood.
For overcoming this problem, there was proposed a pump of the type shown in FIG. 4 which uses permanent magnets for suspending the rotor. As shown, the pump's rotor 21 is provided with permanent magnets 22 and its casing 26 is provided with permanent magnets 23, with like poles of the two sets of permanent magnets facing each other so as to magnetically suspend the rotor 21. In addition, a pivot 25 is formed on the rear surface of an impeller 24 provided at one end of the rotor 21. The rotor 21 and the impeller 24 are thus mechanically supported on the casing 26 at a single point by the pivot 25.
In the prior art artificial heart pump shown in FIG. 4, the blood flow channel 27 for introducing and guiding the flow of blood consists of a hole passing axially through the center of the rotor 21 so as to enable the blood to be passed to near the center of the impeller 24.
It goes without saying that it is inadmissible for an artificial heart pump to promote blood coagulation (thrombogenesis) or blood cell destruction (hemolysis).
Coagulation (thrombogenesis) is likely to occur where there is blood flow stagnation, while blood cell destruction (hemolysis) is apt to occur when blood enters narrow gaps where rotation and sliding arises or at places where a sharp change in the direction of blood flow occurs.
Since the blood flow channel 27 of the prior art artificial heart pump shown in FIG. 4 is provided inside the rotor 21, it is not possible to achieve a sufficient amount of blood flow. Any attempt to increase the amount of blood flow requires an increase in the diameter of the rotor 21 and thus enlarges the size of the artificial heart pump.
Enlarging the diameter of the rotor 21 for increasing the amount of blood flow also leads to a proportional increase in the circumferential velocity of outer surface of the rotor 21. Since this in turn increases the shear force acting on blood entering the suspension gap 28, it promotes hemolysis.
Although this cause for hemolysis can be alleviated by increasing the size of the suspension gap 28, doing this has the effect of increasing the likelihood of thrombogenesis by making it easier for blood to stagnate or flow backward in the suspension gap 28. It is also apt to reduce the pump output.
Since increasing the suspension gap 28 also reduces the magnetic repulsion that maintains it, it makes it difficult to maintain the proper attitude of the rotor 21.
Further, since as shown in FIG. 4 the rotating permanent magnets 22 and the stationary permanent magnets 23 are oriented radially, the magnetic repulsion between them is unstable. This also makes it difficult to maintain the rotor 21 in the proper attitude.
Owing to this radial orientation, moreover, the rotating permanent magnets 22 and the stationary permanent magnets 23 do not impart a force to the rotor 21 in its axial direction. Since this means that no force is produced for holding the pivot 25 in contact with the casing 26, the attitude of the rotor 21 is unstable.
In addition, owing to the configuration of the blood flow channel 27 inside the rotor 21, the blood is forced to flow turbulently through a narrow flow passage. This increases the risk of hemolysis, as does the fact that direction of blood flow is deflected perpendicularly at the time it collides with the impeller 24.
One object of this invention is to provide a pump for a centrifugal type artificial heart which enables securement of a sufficiently large blood flow amount and which does not readily cause blood coagulation or blood cell destruction.
Another object of the invention is to provide a pump for a centrifugal type artificial heart which enables the rotor thereof to be constantly maintained in the proper attitude.